Electrical system



Aug. 31, 1948. T. A. o. GROSS 2,443,028

ELECTRICAL SYSTEM Filed D80. 24, 1945 Mm-firm. 71701105 /2 0. 631%;

Patented Aug. 31, 1948 ELECTRICAL SYSTEM Thomas A. 0. Gross, Waltham, Mass.,

assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application December 24, 1943, Serial No. 515,605

J 9 Claims. I 1 I This invention relates to electrical transformer systems and more particularly to such systems as are responsive to a relatively wide band of frequencies.

In order for a transformer system to be useful over an extended band of frequencies, it is desirable that the product of the distributed capacities and the leakage inductances of the transformer system as a whole be reduced to a minimum. Heretofore, attempts substantially to reduce such capacity-inductance product, in a transformer system in which a substantial ratio exists between the output and the input voltages, have been unsuccessful.

An object of this invention is to devise a transformer system in which the product of the distributed capacity and the leakage inductance thereof is substantially reduced below the maximum values heretofore obtainable.

Another object is to utilize a cascaded transformer arrangement utilizing one or more autotransformers to accomplish the diminishing of said capacity-inductance product.

A further object is to utilize an auto-transformer in the low impedance section of the transformer system to secure the maximum benefits of my invention.

The foregoing and other objects of my invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawing wherein:

Fig. 1 is a diagram of one embodiment of my invention; and

Fig. 2 is a diagram of another embodiment of my invention.

Extended band width or frequency response in a transformer, as pointed out above, can be obtained by reducing the product of the distributed capacity and the leakage inductance of the transformer windings. The leakage inductance in any single transformer can be reduced to a minimum by using a single layer winding each for the primary and the secondary and winding these layers with equal lengths directly one over the other. The effective distributed capacity can also be minimized by polarizing the windings so thatthe voltage difference between the two layers at each point along them is maintained at a minimum. For unity ratio between the number of turns of the primary and secondary windings, the distributed capacity between these windings can be made substantially zero for various types of transformers. As the turns ratio is increased, however, the distributed capacity becomes substantiaL- For purposes of analysis I have divided transformers into two types, the lac-transformer and the auto-transformer. The iso-transformer is one in which separate windings are utilized for' the primary and secondary windings. The autotransformer is one in which the secondary winding includes at least a portion of the primary windings, said windings being called respectively the shunt winding and the series winding.

In an iso-transformer of the above described two-layer type, the distributed capacity between the primary and secondary windings is proportional to where N1 is the number of primary turns and N: is the number of secondary turns. In an autotransformer of the same typ the distributed capacity between the series and shunt windings is proportional to K-2 +1 where N.+ N= From the foregoing it will be seen that with increasing turns ratios the distributed capacity increases rapidly. The auto-transformer inherently has a higher distributed capacity than the isotransformer.

In an iso-transformer of the above type the leakage inductance is proportional to (N9 In an auto-transformer of the above type the leakage inductance is proportional to the square of the number of secondary turns which are not common to the primary. In the usual case in which all of the primary is common to the secondary, this leakage inductance becomes Thus it will be seen that increasing the turns ratios also increases the leakage inductance, said increase being proportionately greater in the auto-transformer. However, the auto-transformer inherently has a lower leakage inductance than the iso-transformer.

The above analysis shows that where a relatively highstep-up ratio between the input and output voltages of a transformer system is desired, the problem of securing a system having a wide band of frequency response is aggravated. If an attempt is made to use a plurality of isotransformer sections in cascade for the purpose oi -maintaining a relatively low ratio of transformation for each section, the distributed-capacitycan be reduced substantially. Under optimum conditions in a two-section cascade, the distributed capacity theoretically can be reduced one half. However, the leakage inductance of such a cascade arrangement as a whole increases to such an extent that no significant reduction in the product of capacity and inductance is se-'- cured. Y

Despite the higher inherent distributed capacity of the auto-transformer, I have found that it can be used in a cascade system with a remarkably great reduction in the capacity-inductance product of the system. This effect is particularly marked where an auto-transformer'is used in a low impedance section and an lac-transformer is used in a high impedance section of such a cascade despite the higher inherent leakage inductance of the iso-transformer.

An arrangement utilizing a pair of auto-transformers in cascade and embodying the principles of my invention is shown diagrammatically in Fig. 1. In this arrangement the transformer system consists of a core member I preferably having a pair of leg sections 2 and 3. The leg section 2 carries a series winding 4 and a shunt winding I. The leg section I carries a series winding 8 and a shunt winding 1. Each of the windings is preferably of the single layer type wound directly one over the other. The series and shunt windings on each leg are likewise preferably of the same length.

The series winding 4 is provided with a pair of end conductors 8 and ilwhich are adapted to be connected to a suitable source of alternating current. It is intended that this source shall have a relatively wide band of frequencies to which it is desired that the transformer system be responsive. The shunt winding ii is wound in the same direction as the series winding 4 and the lower end of said shunt winding is connected by conductor ID to the upper end of conductor 8 of the series winding 4. The upper end of shunt winding is connected by a conductor it to the upper end of the series winding 8. The lower end,

of series winding 6 is connected by conductors l2 and I3 to the lower end of conductor 8 of the series winding 4. Due to the foregoing connections the windings 4 and 5 constitute a step-up auto-transformer. The ratio of transformation may be any suitable value which, however, should be as low as practicable.-

In order that the windings 6 and i may be incorporated on the same core structure as the windings 4.and 6, the series winding 8 is wound in such a direction as to set up a flux which,

passes through the core member 5 in the same direction as the flux set up by the series winding 4. The shunt winding 1 is also wound in the same direction as the series winding 8. The lower end of the shunt winding 1 is connected by a conductor l4 to the upper end of the winding 8.

The upper end of the shunt winding '8 is con-' nected by a conductor IE to one of the output terminals of the transformer system. The lower conductor is is connected to the other output terminal of the transformer system. Due to the foregoing connections the windings 8 and 1' likewise constitute a step-up auto-transformer.

Here likewise the ratio of transformation may be any suitable value which, however, should be as low as practicable.

The arrangement as described above constitutes two step-up transformers in cascade. As pointed out above these two transformers may be incorporated in a single core structure. Qf Wil ie 4 it is to be understood that a seperate core structure could be used for each of these transformers. Transformers built in accordance with the arrangement as shown in Fig. 1 have had their capacity-inductance product substantially reduced below the minimum which has heretofore been possible with prior arrangements. Furthermore transformers of the type as described in Fig. 1 have been able to respond to a greatly increased band of frequencies. I

In order to utilize to a maximum degree the benefits of a cascade containing an auto-transformer section. it is desirable that the auto-transformer be utilized in that portion of the cascade which is connected to the lowest impedance. As higher impedance sections are encountered. it becomes less desirable to use an auto-transformer connection and more desirable to use an lac-transformer connection. Since the lowest impedance section is usually the first step-up section of the cascade, the auto-transformer ispreferably used 'at that point while at one or more succeeding stages the iso-transformer is used, the last or high impedance stage preferably involving an ism-transformer.

A two-stage cascade utilizing the foregoing principles is illustrated in Fig. 2 wherein the same reference numerals are applied where the arrangements are identical with those of Fig. 1. In Fig. 2 it will be seen that the initial transformer, consisting of the windings 4 and I, is an auto-transformer. Associated with the primary winding 6 is a secondary winding 18. This secondary winding is related to its primary in an isotransformer step-up relationship. Therefore, a larger number of turns is utilized in the secondary winding it than in its primary winding 6. Preferably this step-up ratio is substantially higher than for the auto-transformer windings 4-. The lower end of the secondary winding I. may be connected by a conductor I! to the lower end of the primary winding 8. Since the two transformer sections represent successive step-up transformations, it will be seen that the transformer section 4, 5 is a low impedance section and the transformer section fl is a higher impedance section. The arrangement as described in connection with Fig. 2 likewise gives a lower capacity-inductance product and a greatly increased frequency response.

The' reasons for the beneficial effects derived from the cascade arrangement as the type shown in Fig. 2, I believe, are due at least in part to the following. The capacity C effectively connected across the secondary of a transformer is reflected as an equivalent capacitance C. across the primary circuit of the transformer, said equivalent capacitance having a value The inductance L effectively in series with the secondary of a transformer is reflected as an equivalent inductance Le in series with the primary circuit of the transformer, said equivalent inductance having a value Thus the higher the ratio of transformer, the greater will be the effect of the distibuted capacity and the smaller will be the effect of the leakage inductance on the system as a whole. The higher transformation ratios are usually associated with the high impedance portions of a system while the lower transformation ratios are "associated with the lower impedance portions of a system. Thus it will be seen that the higher distributed capacity of the auto-transformer will have a minimum effect when used in a low impedance or low transformation ratio section and the higher leakage inductance of the iso-transformer will have a minimum effect when used in a high impedance or hightransformation ratio section. I have found that by using an autotransformer in a low impedance section of a cascade, the effects of its'distributed capacity can be made negligible, and by using an iso-transformer in a high impedance section of the cascade, the effect of its leakage inductance can be made negligible.

By utilizing the principles as enunciated above I have been able to construct a transformer system having a substantially flat response to frequencies from about 80 cycles per second to several megacycles per second, which response had heretofore been practically impossible.

Of course it is to be understood that this invention is not limited to the particular details as described above as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

' What is claimed is:

1. A transformer system comprising a plurality of voltage changing transformer sections connected in cascade, the section having the lowest ratio of transformation comprising an autotransformer, the section having the highest ratio of transformation comprising an iso-transformer, each of said sections including windings of equal length wound in the same direction, whereby said system has a substantially uniform response over an appreciable frequency band.

2. A transformer system comprising a plurality of voltage changing transformer sections connected in cascade, one transformer section comprising a core member carrying a primary and a secondary winding, another transformer section being an auto-transformer comprising a core member carrying a series and a shunt winding, each of said windings comprising a single layer of turns, the length of the primary winding along its core being substantially equal to the length of the secondary winding along said core, the length ofthe series winding along its core being substantially equal to the length of the shunt winding along said core, the section having the lowest ratio of transformation comprisin the auto-transformer, and the windings of each of s d sections being of equal length and wound in the same direction, whereby said system has a substantially uniform response over an appreciable frequency band.

3. A transformer system comprising a plurality of voltage changing transformer sections connected in cascade, each transformer section being an auto-transformer comprising a core member carrying a series and a shunt winding, said windings being superimposed and each comprising a single layer of turns, the length of the series winding of each section along its core being substantially equal to the length of the winding of its associated shunt winding along said core, and said series and shunt windings being wound in the same direction, whereby said system has a substantially uniform response over an appreciable frequency band.

4. A transformer system comprising a plurality of voltage changing transformer sections connected in cascade, one transformer section being an iso-transformer comprising a core member carrying a primary and a secondary winding, another transformer section being an auto-transformer comprising a core member carrying a series and a shunt winding, each of said windings comprising a single layer of turns, the length of the primary winding along its core being substantially equal to the length of the secondary winding along said core, the length of the series winding along its core being substantially equal to the length of the shunt winding along said core, the section having the lowest ratio of carrying a series and a shunt winding, the seriesand shunt windings of each section being superimposed, of equal length and wound in the same direction on the associated core.

6. A transformer system comprising a, magnetic core, a pair of voltage changing transformer sections connected in cascade, one transformer section comprising a primary and a secondary winding wound on said core. another transformer section being an auto-transformer comprising a series and a, shunt winding wound on said core, the primary and series windings being wound in a direction to send a magnetic flux through said core in the same direction, the section having the lowest ratio of transformation comprising the auto-transformer, and the windings of each of said sections being of equal length and wound in the same direction, whereby said system has a substantially uniform response over an appreciable frequency band.

'7. A transformer system comprising a magnetic core, a pair of voltage changing transformer sections connected in cascade, one transformer section being an iso-transformer comprising a primary and a secondary winding wound on said core, another transformer section being an autotransformer comprising a series .and a shunt winding wound on said core, the primary and series windings being wound in a direction to send a magnetic flux through-said core in the same direction, the section having the lowest ratio of transformation comprising the autotransformer, the section having the highest ratio of transformation comprising the iso-transformer, and the windings of each of said sections being of equal length and wound in the. same direction, whereby said system has a substantially uniform response over an appreciable frequency band.

8. A transformer system comprising a plurality of voltage-changing transformer sections connected in cascade, each of said sections including superimposed equal-length windings wound in the same direction, whereby said system has a substantially uniform response over an appreciable frequency band. 7

9. A transformer system comprising a magnetic core, a pair of voltage changing transformer sections connected in cascade, each transformer section being an auto-transformer comprising a series and a shunt winding wound on said core,

the series windings oi. both or said sections being m STATES Amrs wound in a direction to send a. magnetic flux through said core in the same direction. and the Number I Name Date series and shunt windings of each of said seo- 1,873,975 Meyer-hams Aug. 20, 1932 tiona be;1 superigiipossd. or equal length and 5 1,915,168 Bcharii "June 20, 1933 wound in e some rec ion,

. THOMAS A. 0.03055. FOREIGN Number Country Date REFERENCES CITED 588,851 Germany Nov. 19, 1981 The following references are of record in the a. tile '0! this patent: 

